airfield layout

8/4/2019 Airfield Layout

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Airfield layout

Introduction

Airports were not always

known as airports. They were

originally called "flying

fields". This is because they

were just that, fields. During

the early days of aviation, a

large field was needed for

airplane operations. A long

and equally as wide field wasnecessary because the

airplane needed to be

oriented into the wind no

matter which direction the

wind was blowing.

Airplanes take off and

land more efficiently when

oriented into the wind. To

maximize the airplane's

potential to achieve the

greatest lift in the shortest

amount of distance and time

during takeoff, airplanes

should be pointed into the

wind. By landing into the

wind the ground speed is

minimized. This allows the

pilot more time to make the

adjustments necessary for a

smooth touchdown. Ground

speed is a combination of

airspeed (the speed provided

by the propulsion system's

thrust minus some drag) plus

wind speed. Therefore if an

airplane with an airspeed of

100 mph is landing with a

wind that has a speed of 20

mph then the actual ground

speed of the airplane is 120

mph (100 mph + 20 mph =



120 mph). Conversely, if the

airplane with an airspeed of

100 mph is landing into the

wind with a wind speed of 20

mph then the actual groundspeed of the airplane is 80

mph (100 mph - 20 mph = 80

mph). This is helpful to the

pilot as the pilot attempts to

stall the airplane just above

the runway for a smooth

landing.

In early aviation times, thetakeoff procedure consisted

of people moving the airplane

to the downwind side of the

field and pointing it into the

wind. Early aircraft were

designed to fly, not move

about the ground, so the

landing gear of many

airplanes were merely skids,

not wheels. After the airplane

was checked out to see if

everything was ready, the

pilot switched on the fuel and

the magneto. A helper would

turn the propeller by hand

while others held onto the

airplane to keep it from

moving. When the engine

started and the helper who

"propped" the plane was out

of the way, the airplane was

released, bounced awkwardly

along the field and eventually

took off. Since the wind speed

and direction varied, a large

field allowed the airplane to

always takeoff and land into

the wind. Not until after the

1930s were airplanes

equipped for self-propelled

taxiing (move slowly along

the ground) and quite a few



airports were still large fields.

Runway orientation

In navigation and surveying, all measurement of

ection is performed by using the numbers of a compass.

compass is a 360° circle where 0/360° is North, 90° is

st, 180° is South, and 270° is West. Runways are laid out

cording to the numbers on a compass. A runway's

mpass direction is indicated by a large number painted at

e end of each runway. Preceding that number are 8 white

pes. Following that number by 500 feet is the

uchdown zone" which is identified by 6 white stripes. A

nway's number is not written in degrees, but is given a

orthand format. For example, a runway with a marking of

4" is actually close to (if not a direct heading of) 140

grees. This is a southeast compass heading. A runway

h a marking of "31" has a compass heading of 310

grees, that is, a northwest direction. For simplicity, the

A rounds off the precise heading to the nearest tens.

r example, runway 7 might have a precise heading of 68

grees, but is rounded off to 70 degrees.



Each runway has a different number on each end. One end of the runway as shown

below is facing due west while the other end of the runway is facing due east. The

compass direction for due west is 270 degrees ("27"). The compass direction for due east

is 90 degrees ("9"). All runways follow this directional layout. This runway would be

referred to as "Runway 9-27" because of its east-west orientation.



The FAA includes over 20 different runway layouts in their advisory materials. There are 4

basic runway configurations with the rest being variations of the original patterns. The

basic runway configurations are the following:

Single runway

This is the simplest of the 4 basic configurations. It is one runway optimally positioned for prevailing winds,

noise, land use and other determining factors. During VFR (visual flight rules) conditions, this one runway

should accommodate up to 99 light aircraft operations per hour. While under IFR (instrument flight rules)

conditions, it would accommodate between 42 to 53 operations per hour depending on the mix of traffic and

navigational aids available at that airport.

Parallel runways

There are 4 types of parallel runways. These are named according to how closely

they are placed next to each other. Operations per hour will vary depending on the total



number of runways and the mix of aircraft. In IFR conditions for predominantly light

aircraft, the number of operations would range between 64 to 128 per hour



Open-V runways

Two runways that diverge from different directions but do NOT intersect form a shape that looks like an

"open-V" are called open-V runways. This configuration is useful when there is little to no wind as it allows

for both runways to be used at the same time. When the winds become strong in one direction, then only one

runway will be used.

When takeoffs and landings are made away from the two closer ends, the number of operations per hour

significantly increases. When takeoffs and landings are made toward the two closer ends, the number of

operations per hour can be reduced by 50%.

Intersecting runways

Two or more runways that cross each other are classified as intersecting runways. This type of configuration isused when there are relatively strong prevailing winds from more than one direction during the year. When the

winds are strong from one direction, operations will be limited to only one runway. With relatively light

winds, both runways can be used simultaneously. The greatest capacity for operations is accomplished when



the intersection is close to the takeoff end and the landing threshold as shown below (with the configuration

on the left).

The capacity for the number of operations varies greatly with this runway configuration. It

really depends on the location of the intersection and the manner in which the runways

are operated (IFR, VFR, aircraft mix). This type of configuration also has the potential to

use a greater amount of land area than parallel runway configurations.

Airports also use standardized lighting and ground markings to provide direction

and identification to all air and ground crews. To assist pilots in differentiating at nightbetween airport runways and freeways, airports have rotating beacon lights. These

beacons usually flash green and white lights to indicate a civilian airport. They are visible



from the air long before the entire airport is recognizable. To help pilots at night quickly

identify the beginning of a runway, green threshold lights line the runway's edge. Red

lights mark the ends of runways and indicate obstructions. Blue lights run alongside

taxiways while runways have white or yellow lights marking their edges. All these

markings and lights serve to set a safety standard for all pilots to follow.

Runway layouts and orientation differ a great deal. The design of

airports accordingly varies depending upon geography, local

environment and number of operations. College Park Airport (CGS)

just north of Washington, DC is a small community airport. Shown

below left, it is no different than many small airports with one majorexception. College Park Airport is the world's oldest continuously



operated airport. It has been in operation since 1909. College Park

Airport began operation just six years after the Wright Brothers first

flew a heavier-than-air airplane. Since College Park Airport's

inception, airports have evolved from large vacant fields to concrete

mini-cities with thousands of workers and passengers. The airfieldto the right below is a rural strip in a intersecting V pattern.

Influences on Airport Layout

When runways are built, their layout is influenced by many factors:

• ICAO Regulations

• Environmental concerns

• Noise level impacts

• Terrain and soil considerations

• Natural and man-made obstructions

• Annual weather patterns

• Size and performance characteristics of the airplanes that will use the runways

The ground on which the airport is to be built must have a stable stratum of earth upon which

building foundations can be anchored. The soil must be capable of supporting heavy loads without

shifting or sinking. If the airport's runways are to be used by heavy aircraft (airplanes with a gross

weight 300,000 pounds and heavier) the underlying soil and/or bedrock must be able to support the

weight of the runway plus the aircraft's weight. Many airport runways have several feet of reinforced

concrete to support the airplanes without cracking.

Land at a greater elevation surrounding an airport such as mountains also have a profound effect on

winds. In the daytime, air next to a mountain slope is heated by contact with the ground as it receives

radiation from the sun. This air usually becomes warmer than the air farther up the slope. Colder,

denser air in the area settles downward and forces the warmer air near the ground up the mountainslope. This wind is called a "valley wind" because the air is flowing up and out of the valley. At night,

the air in contact with the mountain slope is cooled by terrestrial radiation and becomes heavier than



the surrounding air. It sinks along the slope producing the "mountain wind" which flows like water

down the mountain slope. Mountain winds are usually stronger than valley winds, especially in winter.

The wind pattern on the leeward side of a mountain contains dangerous downdrafts or "rotor waves".

An aircraft flying through such wind would encounter hazardous turbulence that would push the

airplane towards the ground. These are all considered when orienting runways in an area near

mountains.

There are many airports within mountainous areas where the runway headings generally run

parallel with the length of the valley in which they are located or run along neighboring rivers. The

terrain often influences development of the runways in the mountains.

Man-made obstructions like multi-storied high rises, transmissions towers and bridges can and

do influence runway orientation. Landing at Reagan National Airport on Runway 15 requires a curvingapproach that follows above the Potomac River's course. Takeoff on Runway 33 from the same airport

requires the reverse trip following above the Potomac River because of government buildings to the

north of the river and many high buildings south of the river.

Consideration of local weather patterns is also a factor in determining an airport's layout. The

weather patterns of an area, especially the prevailing winds, are a major factor in determining runway

headings. Prevailing winds are defined as the direction from which the winds blow most frequently.Many airfields have runways facing a variety of directions. The purpose of this is to

provide arriving aircraft with the best runway to land on, according to the wind direction.

Runway orientation is determined from historical data of the prevailing winds in the area.

This is especially important for single-runway airports that don't have the option of a

second runway pointed in an alternative direction. A common scenario is to have two

runways arranged at or close to 90 degrees to one another, so that aircraft can always

find a suitable runway. Almost all runways are reversible, and aircraft use whichever

runway in whichever direction is best suited to the wind. In light and variable wind

conditions, the direction of the runway in use might change several times during the day.



Airfield Layout, Markings and Signals

Airfield Identification

A signal square which can be seen from the air. It identifies the airfield using a lettered code. It

has now been replaced by radio contact, and a three letter flight planning code.

Airfield Identification Beacon

A flashing beacon which used a unique code to indicate each airfield. It is not used nowadays.

Aircraft Servicing Platform

An area reserved for pre and post flight checks to aircraft, and parking for aircraft between

flights.

Arrester Gear and Barriers

Arrester Gear is a cable stretched across the end of a runway (similar to those on an aircraftcarrier) but for emergency use only. It can only be used with certain types of aircraft. A barrier

is a large safety net to stop aircraft in an emergency.

Dispersal Hard Standing (Military Airfield Only)

Parking areas for aircraft away from the main hangar/runway area to minimise damage to

aircraft during a ground attack.

Fire Station

Area close to the airfield where emergency service vehicles are kept.

Hangar Large building used to house aircraft undergoing general maintenance and/or repairs.

Holding Points

Aircraft have to stop at the holding points on the taxiway to wait for permission from the

Control Tower before they can proceed down the runway.

Main Runway

The most frequently used runway. The direction of the prevailing wind will dictate which

runway this is. Aircraft take-off and land into the wind.

Operational Readiness Platform (Military Airfields Only)Area for parking aircraft on quick reaction alert so they can have immediate access to the

runway if necessary.

Secondary Runway

A second runway which is used when the wind changes from its normal direction.

Sterile Area

The beginning of the runway, before the threshold markings, where nothing can be parked.

Terminal Building

Building for handling passengers and may contain Immigration Control and Customs.



Threshold Markings

Marks the beginning of the usable runway.

Windsock

Bright orange tubes which will fly in the wind to indicate its direction.

Aircraft stand

A designated area on an apron intended to be used for parking an aircraft.

Apron

A defined area on airfield intended to accommodate aircraft for purposes of loading or

unloading passengers, mail or cargo, fuelling, parking or maintenance.

Apron management service

A service provided to regulate the activities and the movement of aircraft and vehicles on an

apron.

Barrette

Three or more aeronautical ground lights closely spaced in a transverse line so that from a

distance they appear as a short bar of light.

Heliport

An aerodrome or a defined area on a structure intended to be used wholly or in part for thearrival, departure and surface movement of helicopters.

Displaced threshold

A threshold not located at the extremity of a runway.

Manoeuvring area

That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, excluding

aprons.

Marker

An object displayed above ground level in order to indicate an obstacle or delineate a boundary.

Marking

A symbol or group of symbols displayed on the surface of the movement area in order to

convey aeronautical information.



Movement area

That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, consisting

of the manoeuvring area and the apron(s).

Pavement classification number (PCN)

A number expressing the bearing strength of a pavement for unrestricted operations.

Obstacle

All fixed (whether temporary or permanent) and mobile objects, or parts thereof, that are

located on an area intended for the surface movement of aircraft or that extend above a defined

surface intended to protect aircraft in flight.

Intermediate holding position

A designated position intended for traffic control at which taxiing aircraft and vehicles shall

stop and hold until further cleared to proceed, when so instructed by the aerodrome control

tower.

Landing area

That part of a movement area intended for the landing or take-off of aircraft.

Landing direction indicator

A device to indicate visually the direction currently designated for landing and for take-off.

Runway visual range(RVR)

The range over which the pilot of an aircraft on the centre line of a runway can see the runway

surface markings or the lights delineating the runway or identifying its centreline.

Shoulder

An area adjacent to the edge of a pavement so prepared as to provide a transition between the

pavement and the adjacent surface.

Taxiway

A defined path on a land aerodrome established for the taxiing of aircraft and intended to

provide a link between one part of the aerodrome and another.

Threshold

The beginning of that portion of the runway usable for landing.

Touchdown zone

The portion of a runway, beyond the threshold, where landing aeroplanes f irst contact the

runway.



Airfield traffic pattern

An airfield traffic pattern is a standard path followed by aircraft when taking off or

landing. At an airport, the pattern (or circuit) is a standard path for coordinating air

traffic. It differs from "straight in approaches" and "direct climb outs" in that aircraft using

a traffic pattern remain close to the airport. Patterns are usually employed at small

general aviation (GA) airfields and military airbases. Most large airports avoid the system,

unless there is GA activity as well as commercial flights. However, a pattern of sorts is

used at airports in some cases, such as when an aircraft is required to go around.

Pilots prefer to take off and land facing into the wind. This has the effect of

reducing aircraft speed over ground and hence reducing the distance required to perform

either manoeuvre. The exception to this rule is at alpine airports, 'Altiports' where the

runway is on a severe slope. In these instances, takeoffs are made downhill and landings

uphill, with the slope aiding in acceleration and deceleration.

Traffic patterns can be defined as left-hand or right-hand, according to which way the turns in

the pattern lie. They are usually left-hand because most small airplanes are piloted from the left seat (or

the senior pilot or pilot in command sits in the left seat), and so the pilot has better visibility out the left

window. Right-hand patterns will be set up for parallel runways, for noise abatement or because of

ground features (such as terrain, towers, etc.). Unless noted in the Airport Facilities Directory or on a

Sectional Chart, all traffic patterns at non-towered airports are to the left.

Helicopters are encouraged, but not required, to use an opposite pattern from fixed-wing traffic due

to their slower speed and greater maneuverability. Because the active runway is chosen to meet the

wind at the nearest angle (upwind), the pattern orientation also depends on wind direction. Patterns are

typically rectangular in basic shape, and include the runway along one long side of the rectangle. Each

leg of the pattern has a particular name.

• The section extending from the runway ahead is called the departure leg in the US, and

sometimes elsewhere upwind leg . (In the US, upwind properly refers to an approach leg outside

the downwind leg and in the opposite direction.)

• The first short side is called the crosswind leg .

• The long side parallel to the runway but flown in the opposite direction is called the downwind

leg . (This leg also consists of three sub-legs. They are Early downwind, Mid Downwind and

late downwind)

• The short side ahead of the runway is called the base leg .

• The section from the end of base leg to the start of the runway is called the final approach or

final . The last section of the final approach is sometimes referred to as short final .



expect other air traffic, and be able to see it and avoid it. GA pilots flying under Visual

Flight Rules (VFR) will not be separated by air traffic control, and so the pattern is a vital

way to keep things orderly. However, at tower-controlled airports air traffic control (ATC)

will provide traffic advisories for VFR flights on a work-load permitting basis.

If an aircraft intending to land must be delayed, the air traffic control (ATC) may

decide to place it in a holding pattern until the airport is prepared to permit the landing.

Commercial aircraft on hold will generally fly slow, racetrack-shaped patterns which differ

considerably from the airfield traffic pattern that will be commenced once the approval

has been given to land. Although an aircraft in a holding pattern may similarly circle the

airport, ATC may designate a distant location in which to circle.

airfield layout

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